U.S. patent number 7,075,691 [Application Number 10/923,668] was granted by the patent office on 2006-07-11 for complex lens for a tandem scanning optical system and a manufacturing method thereof.
This patent grant is currently assigned to PENTAX Corporation. Invention is credited to Junji Kamikubo, Daisuke Koreeda.
United States Patent |
7,075,691 |
Koreeda , et al. |
July 11, 2006 |
Complex lens for a tandem scanning optical system and a
manufacturing method thereof
Abstract
A complex lens for a tandem scanning optical system converges a
plurality of light beams, which are modulated independently and
deflected by a deflector, onto a surface to be scanned, and forms a
plurality of scanning lines at the same time. The complex lens
includes a plurality of stacked lens portions that are molded as a
single-piece element. Thus a plurality of lens surfaces of the lens
portions at an incident side are formed by a single-piece mirror
surface core and a plurality of lens surfaces of the lens portions
at an exit side are formed by another single-piece mirror surface
core during the molding process.
Inventors: |
Koreeda; Daisuke (Tokyo,
JP), Kamikubo; Junji (Tokyo, JP) |
Assignee: |
PENTAX Corporation (Tokyo,
JP)
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Family
ID: |
18830690 |
Appl.
No.: |
10/923,668 |
Filed: |
August 24, 2004 |
Prior Publication Data
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Document
Identifier |
Publication Date |
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US 20050024723 A1 |
Feb 3, 2005 |
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Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
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09987871 |
Nov 16, 2001 |
6790389 |
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Foreign Application Priority Data
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Nov 27, 2000 [JP] |
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2000-358852 |
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Current U.S.
Class: |
359/205.1;
359/204.2 |
Current CPC
Class: |
G02B
3/0025 (20130101); G02B 3/0031 (20130101); G02B
3/0068 (20130101); G02B 3/0075 (20130101); G02B
26/123 (20130101); G02B 3/005 (20130101); Y10S
425/808 (20130101) |
Current International
Class: |
G02B
26/08 (20060101) |
Field of
Search: |
;359/205-208 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Cherry; Euncha P.
Attorney, Agent or Firm: Greenblum & Bernstein
P.L.C.
Parent Case Text
This application is a divisional of U.S. patent application Ser.
No. 09/987,871, filed Nov. 16, 2001 now U.S. Pat. No. 6,790,389,
the disclosure of which is expressly incorporated herein by
reference in its entirety.
Claims
What is claimed is:
1. A complex lens for a tandem scanning optical system that
converges a plurality of light beams, which are modulated
independently and deflected by a single deflector, onto a surface
to be scanned, to scan a plurality of lines on the surface at the
same time, said complex lens comprising: a plurality of stacked
lens portions that are molded as a single-piece element, wherein a
plurality of lens surfaces of said lens portions at an incident
side are formed by a first single-piece mirror surface core and a
plurality of lens surfaces of said lens portions at an exit side
are formed by a second single-piece mirror surface core during the
molding, each of the first and second single-piece mirror surface
cores having a plurality of mirror surface portions, the plurality
of mirror surface portions of the first single-piece mirror surface
core respectively forming a plurality of lens surfaces at the
incident side, the plurality of mirror surface portions of the
second single-piece mirror surface core respectively forming a
plurality of lens surfaces at the exit side, wherein the plurality
of lens surfaces on the incident side and on the exit side are
configured to be spaced in a direction transverse to a scan
direction.
2. The complex lens according to claim 1, wherein each of said lens
portions has a convex sectional shape in a direction perpendicular
to the direction in which a plurality of light beams scan.
3. The complex lens according to claim 1, wherein said lens
surfaces of at least one of the incident and exit sides are formed
as rotationally-symmetrical convex surfaces with respect to
respective optical axes.
4. The complex lens according to claim 1, said stacked lens
portions being integrally molded.
Description
BACKGROUND OF THE INVENTION
The present invention relates to a complex lens that consists of a
plurality of stacked lens portions, and particularly, relates to
the complex lens for a tandem scanning optical system employed in
an imaging device such as a color laser printer for converging a
plurality of light beams deflected by a deflector. Further, the
present invention relates to a manufacturing method of such a
complex lens for a tandem scanning optical system.
A tandem scanning optical system employed in a color laser printer
is provided with four semiconductor lasers and four photoconductive
drums that correspond to colors Y (Yellow), M (Magenta), C (Cyan)
and K (blacK), respectively. In such a tandem scanning optical
system, it is preferable to make at least one part of the optical
system shareable among the colors to downsize the system. The
polygon mirror may be shared.
When a polygon mirror is shared, four light beams are incident on
the polygon mirror such that they are arranged in an auxiliary
scanning direction, which is coincident with a direction of the
rotation axis of the polygon mirror. The four light beams deflected
by the polygon mirror are converged by an f.theta. lens and the
optical paths thereof are separated by mirrors. The separated four
light beams form scanning lines on the respective photoconductive
drums.
It is preferable that the four light beams deflected by the polygon
mirror are converged by the respective lens elements in order to
obtain the most suitable optical performance. On the other hand,
the smaller the thickness of the polygon mirror is, the smaller the
spaces among the four light beams are in the vicinity of the
polygon mirror. This does not allow employing independent lens
elements for the respective light beams. Therefore, a lens in the
f.theta. e lens arranged close to the polygon mirror should be a
complex lens that consists of stacked four lens portions.
SUMMARY OF THE INVENTION
It is therefore an object of the invention to provide an improved
manufacturing method of a complex lens for a tandem scanning
optical system that is capable of reducing the positional error
among the lens portions when the complex lens that consists of
stacked lens portions is molded as a single-piece element.
For the above object, according to the present invention, there is
provided a manufacturing method of a complex lens for a tandem
scanning optical system, including a step for preparing molding
dies for forming a cavity to form the complex lens as a
single-piece element, and a step for injecting lens material into
the cavity. The molding dies include a pair of single-piece mirror
surface cores that form a plurality of lens surfaces of the complex
lens at an incident side and a plurality of lens surfaces at an
exit side, respectively. The complex lens consists of a plurality
of stacked lens portions for converging a plurality of light beams,
which are modulated independently and deflected by a deflector,
onto a surface to be scanned, respectively, for forming a plurality
of scanning lines at the same time.
Further, a complex lens for a tandem scanning optical system
according to the present invention is formed as a single-piece
element that is equivalent to a combination of independent lens
portions stacked one on another, the lens surfaces of the lens
portions at the incident side are formed by a single-piece mirror
surface core and the lens surface of the lens portions at the exit
side are formed by another single-piece mirror surface core.
Since the lens surfaces at the incident side and the lens surface
at the exit side are formed by the single-piece mirror surface
cores, respectively, during the molding process, the relative
positional error among the lens surfaces at the incident side and
that at the exit side can be reduced.
It is preferable that each of the mirror surface portions of the
mirror surface cores has a concave sectional shape in a direction
perpendicular to the direction in which a plurality of light beams
scan (i.e., an auxiliary scanning direction). That is, the lens
surfaces of the molded complex lens preferably have convex
sectional shapes in the direction perpendicular to the scanning
direction of the light beam.
When the mirror surface portions of the mirror surface core have
convex sectional shapes, the boundary of the mirror surface
portions will be a valley. Therefore, the boundary portions cannot
be sharply processed because of the limitation of a cutting tool,
which requires predetermined margins at the boundaries. The margins
are not employed as lens surfaces.
On the other hand, when the mirror surface portions of the mirror
surface core have concave sectional shapes, the boundary of the
mirror surface portions will be a peak. Therefore, since the
boundary portions can be sharply processed by the cutting tool, the
mirror surface portions can be processed without the margins.
The mirror surface portions of at least one of the mirror surface
cores at the incident and exit sides may be formed as
rotationally-symmetrical concave surfaces with respect to
respective optical axes such as spherical surfaces. In such a case,
the lens surfaces of at least one of the incident and exit sides
are formed as rotationally-symmetrical convex surfaces with respect
to respective optical axes.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1A is a sectional view of a cavity and surroundings of an
injection molding machine to mold a complex lens for a tandem
scanning optical system according to embodiments;
FIG. 1B is a sectional view of the complex lens molded by the
injection molding machine of FIG. 1A;
FIG. 2 is a perspective view of a mirror surface core employed in
the injection molding machine of FIG. 1A;
FIG. 3 is a sectional view of the injection molding machine to mold
the complex lens of the embodiments;
FIG. 4 shows a tandem scanning optical system that employs the
complex lens of FIG. 1B in the auxiliary scanning direction;
FIG. 5 shows a scanning optical system of a first embodiment in the
main scanning direction;
FIG. 6 shows the scanning optical system of the first embodiment in
the auxiliary scanning direction;
FIG. 7A is a graph showing a linearity error of the scanning
optical system of the first embodiment;
FIG. 7B is a graph showing a curvature of field of the scanning
optical system of the first embodiment;
FIG. 8 shows a scanning optical system of a second embodiment in
the main scanning direction;
FIG. 9 shows the scanning optical system of the second embodiment
in the auxiliary scanning direction;
FIG. 10A is a graph showing a linearity error of the scanning
optical system of the second embodiment; and
FIG. 10B is a graph showing a curvature of field of the scanning
optical system of the second embodiment.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
A method for manufacturing a complex lens for a tandem scanning
optical system will be described with reference to FIGS. 1 through
3. FIG. 1A is a sectional view of a cavity and surroundings of an
injection molding machine to mold the complex lens according to
embodiments; FIG. 1B is a sectional view of the molded complex
lens; FIG. 2 is a perspective view of a mirror surface core; and
FIG. 3 is a sectional view of the injection molding machine.
The complex lens is formed as a single-piece element through an
injection molding process. Molding dies used in the process include
cores having mirror-finished surfaces to form incident lens
surfaces and exit lens surfaces of the lens portions. The core is
called a "mirror surface core" in this specification.
The general construction of the injection molding machine will be
described with reference to FIG. 3. The machine is provided with
first and second retainer plates 2 and 3 that can slide in a
right-left direction in the drawing in cylinders 1a and 1b located
at right and left sides. The retainer plates 2 and 3 have hollows
at the faces opposed to each other and mirror surface cores 4 and 5
are installed in the hollows, respectively. A cavity 6 is formed as
a space surrounded by molding dies, which include the first and
second retainer plates 2, 3, and the mirror surface cores 4 and 5,
when the retainer plates 2 and 3 close to contact with each other.
Further, the first and second retainer plates 2 and 3 are connected
with driving rods 7 and 8, respectively, and the movement of the
rods 7 and 8 in the right-left direction drives the retainer plates
2 and 3 to close them up and to move them away.
During the molding process, as shown in FIG. 3, the first and
second retainer plates 2 and 3 get closer to contact with each
other and molten resin is injected into the cavity 6 through a
runner (not shown). After the predetermined cooling time is elapsed
from the injection, the retainer plates 2 and 3 are moved away and
the molded complex lens is retrieved from the molding dies.
The molded complex lens 20 is formed as a single-piece element that
is equivalent to a combination of independent four lens portions
stacked one on another, as shown in FIG. 1B. The complex lens 20
has four incident lens surfaces 21 and four exit lens surfaces 22.
In FIG. 1B, an x-direction is a direction parallel to each of
optical axes of the lens portions, a y-direction is a direction
along which the light beams are deflected by a polygon mirror
(referred to as a main scanning direction), and a z-direction is a
direction perpendicular to the x- and y-directions (referred to as
an auxiliary scanning direction). The incident lens surfaces 21 and
the exit lens surfaces 22 have convex sectional shapes in the
auxiliary scanning direction. Further, in FIG. 1B, the convex
shapes of the lens surfaces are exaggerated for purposes of
illustration.
The incident lens surfaces 21 are formed (i.e., molded) by the
single-piece mirror surface core 4 and the exit lens surfaces 22
are formed (i.e., molded) by the single-piece mirror surface core
5. As shown in FIG. 1A and FIG. 2, the mirror surface core 4 is
formed as a single-piece element and is provided with four mirror
surface portions 4a that are formed independently to form four lens
surfaces. The mirror surface portions 4a have concave sectional
shapes in both of the main and auxiliary scanning directions. The
other mirror surface core 5 is formed as a single-piece element and
is provided with four mirror surface portions 5a that have concave
sectional shapes in at least the auxiliary scanning direction.
If the mirror surface cores are independent of one another (i.e.,
one core corresponds to one lens surface), there may be relative
positional errors among the respective mirror surface cores. Since
the positional error of the cores results in the positional error
among the lens surfaces of the molded complex lens, the image
forming performance deteriorates.
On the other hand, since the incident lens surfaces 21 and the exit
lens surfaces 22 are formed by the single-piece mirror surface
cores 4 and 5, respectively, during the molding process, the
relative positional error among the incident lens surfaces 21 and
the relative positional error among the exit lens surfaces 22 can
be reduced. Further, since the mirror surface portions 4a and 5a
have concave sectional shapes in the auxiliary scanning direction,
each of the boundaries of the mirror surface portions 4a and 5a are
formed as a peak that can be sharply processed by the cutting tool.
Therefore, the mirror surface portions can be processed without the
margins at the boundary portions, which avoids upsizing of the lens
surfaces 21 and 22 in the auxiliary scanning direction more than
necessary.
FIG. 4 is a general description of a tandem scanning optical
system, which employs the complex lens manufactured by the
above-described method, in the auxiliary scanning direction.
The tandem scanning optical system deflects the four laser beams,
which are emitted from light source portion (not shown) and
modulated independently, by means of a polygon mirror 30 at the
same time, and converges the four laser beams onto the respective
photoconductive drums 41, 42, 43 and 44. Rotation of the polygon
mirror 30 about a rotation axis 30a scans the laser beam on the
photoconductive drums to form four scanning lines at the same
time.
An f.theta. lens to converge the light beams consists of a first
lens 51 and a second lens 52 that are located in the vicinity of
the polygon mirror 30, and third lenses 53a, 53b, 53c and 53d that
are located on the respective optical paths divided by mirrors 71
to 78. The first and second lenses 51 and 52 are the complex
lenses, each of which is formed as a single-piece element and it is
equivalent to the combination of four independent lens portions
stacked one on another as shown in FIG. 1B. Further, each of the
lens surfaces of the first and second lens 51 and 52 seems like a
flat surface in FIG. 4, while it is not flat surface. Each of the
surfaces of the first and second lenses 51 and 52 is a combination
surface having four lens portions.
In FIG. 4, the laser beam deflected by the polygon mirror 30 at the
highest point among the four laser beams passes through the highest
lens portions of the first and second lenses 51 and 52. The laser
beam is reflected by the mirror 71 upwards and then reflected by
the mirror 72 downwards. The reflected laser beam passes through
the third lens 53a and is converged onto the photoconductive drum
41. In the same manner, the second, third and fourth laser beams
from the top pass the second, third fourth lens portions of the
first and second lenses 51 and 52, and they are reflected by the
mirrors 73, 75 and 77 to the upside and then reflected by the
mirrors 74, 76 and 78 to the downside, respectively. The reflected
second, third and fourth laser beams pass through the third lenses
53b, 53c and 53d and are converged onto the photoconductive drums
42, 43 and 44, respectively.
Next, two embodiments of the tandem scanning optical system whose
generic constructions are shown in FIG. 4 will be described. In the
following description, the optical system for the first laser beam
deflected by the polygon mirror 30 at the highest point is taken
out from the four optical systems. Further, the optical path is
developed by omitting the mirrors 71 and 72.
First Embodiment
FIGS. 5 and 6 show a scanning optical system of a first embodiment
in the main scanning direction and in the auxiliary scanning
direction, respectively. FIG. 5 shows optical elements from a
cylindrical lens 31 to the photoconductive drum 41; and FIG. 6
shows optical elements from the polygon mirror 30 to the
photoconductive drum 41.
The following TABLE 1 shows the numerical construction of the
scanning optical system according to the first embodiment.
Symbol f in the table represents a focal length of the f.theta.
lens in the main scanning direction, W represents the width of the
scanning range, ry is a radius of curvature (unit: mm) of a surface
in the main scanning direction, rz denotes a radius of curvature
(unit: mm) of a surface in the auxiliary scanning direction (which
will be omitted if a surface is a rotationally-symmetrical
surface), d is a distance (unit: mm) between surfaces along the
optical axis, n is a refractive index of an element at a design
wavelength 780 nm.
Surface numbers 1 and 2 represent the cylindrical lens 31, a number
3 represents the reflection surface of the polygon mirror 30,
numbers 4 and 5 represent the first lens 51 of the f.theta. lens,
numbers 6 and 7 represent the second lens 52 of the f.theta. lens,
numbers 8 and 9 represent the third lens 53 a of the f.theta.
lens.
TABLE-US-00001 TABLE 1 f = 200.0 mm W = 216 mm Surface Number ry rz
d n 1 .infin. 50.00 4.00 1.51072 2 .infin. -- 97.00 3 .infin. --
33.00 4 .infin. -- 10.00 1.48617 5 -199.80 -- 4.00 6 .infin. --
10.00 1.48617 7 -170.00 -- 93.00 8 -540.00 30.38 4.00 1.48617 9
-1045.00 -- 95.10
The surface of number 1 is a cylindrical surface having a power
only in the auxiliary scanning direction, the surfaces of numbers 2
and 3 are flat surfaces, the surfaces of numbers 4, 5, 6, 7 and 9
are rotationally-symmetrical aspherical surfaces, and the surface
of number 8 is an anamorphic aspherical surface.
A rotationally-symmetrical aspherical surface is defined by
distribution of sag amount X(h). The sag X(h) is a distance of the
point on the aspherical surface whose distance from the optical
axis is h with respect to the tangential plane at the optical axis.
The sags X(h) is expressed by the following equation (1);
.function..kappa..times..times..times..times..times.
##EQU00001##
Symbol C is a curvature (1/ r) on the optical axis, .kappa. is a
constant, A4, A6 and A8 are aspherical surface coefficients of
fourth, sixth and eighth orders.
The various constants and coefficients for defining the
rotationally-symmetrical surfaces are shown in TABLE 2.
TABLE-US-00002 TABLE 2 Surface Number .kappa. A.sub.4 A.sub.6
A.sub.8 4 0.00 3.58 .times. 10.sup.-6 -5.09 .times. 10.sup.-10 0.00
5 0.00 2.84 .times. 10.sup.-6 -1.33 .times. 10.sup.-10 1.00 .times.
10.sup.-14 6 0.00 1.03 .times. 10.sup.-6 1.96 .times. 10.sup.-11
0.00 7 0.00 1.06 .times. 10.sup.-6 3.00 .times. 10.sup.-10 0.00 9
0.00 -4.47 .times. 10.sup.-8 -1.53 .times. 10.sup.-12 -1.49 .times.
10.sup.-16
It should be noted that the radii of curvature of the aspherical
surfaces indicated in TABLE 1 are values on the optical axis.
The anamorphic aspherical surface (surface number 8 ) is a surface
whose radius of curvature in the auxiliary scanning direction is
determined by the distance from the optical axis in the main
scanning direction and it does not have a rotation axis. The
anamorphic aspherical surface is defined by the following two
equations (2) and (3).
.function..kappa..times..times..times..times..times..times..function..tim-
es..times..times..times. ##EQU00002##
The shape of the anamorphic aspherical surface in the main scanning
direction is defined by the sag X(Y) according to the equation (2).
The sag X(Y) is a distance of the point on the aspherical surface
whose distance from the optical axis is Y in the main scanning
direction with respect to the tangential plane at the optical
axis.
A radius of curvature in the auxiliary scanning direction varies in
accordance with the distance Y from the optical axis in the main
scanning direction. The radius of curvature rz(Y) of the surface in
the auxiliary scanning direction at the point where the distance
from the optical axis is Y is expressed by the equation (3).
Symbols in the equation (2) are the same as in the equation (1).
The values B.sub.1, B.sub.2, B.sub.4 and B.sub.6 are coefficients
that define the radius of curvature in the auxiliary scanning
direction, rz.sub.0 is a radius of curvature in the auxiliary
scanning direction on the optical axis (equal to rz in TABLE 1).
The coefficients that define the surface of number 8 are shown in
TABLE 3.
TABLE-US-00003 TABLE 3 .kappa. 0.00 B.sub.1 -1.89 .times.
10.sup.-06 A.sub.4 1.08 .times. 10.sup.-07 B.sub.2 -1.16 .times.
10.sup.-06 A.sub.6 -1.08 .times. 10.sup.-11 B.sub.4 5.36 .times.
10.sup.-12 A.sub.8 3.88 .times. 10.sup.-16 B.sub.6 2.52 .times.
10.sup.-15 A.sub.10 0.00 -- --
FIGS. 7A and 7B are graphs showing the optical performance of the
scanning optical system of the first embodiment; FIG. 7A shows a
linearity error that is a deviation of the real beam spot with
respect to the ideal beam spot in the main scanning direction; and
FIG. 7B shows a curvature of field that is a distance from the
design image surface to the beam waist. In the graph of FIG. 7B, a
dotted line indicates the values in the main-scanning direction and
a solid line indicates the values in the auxiliary scanning
direction.
Second Embodiment
FIGS. 8 and 9 show a scanning optical system of a second embodiment
in the main scanning direction and in the auxiliary scanning
direction, respectively. The following TABLE 4 shows the numerical
construction of the scanning optical system according to the second
embodiment. The relationship between the surface numbers and the
optical elements are identical to the first embodiment.
TABLE-US-00004 TABLE 4 f = 200.0 mm W = 216 mm Surface Number Ry rz
d n 1 .infin. 50.00 4.00 1.51072 2 .infin. -- 97.00 3 .infin. --
46.50 4 -75.00 1000.00 5.00 1.48617 5 -69.10 -400.70 2.00 6 .infin.
-- 10.00 1.51072 7 -115.80 .infin. 106.50 8 -722.70 29.71 4.00
1.48617 9 -1750.80 -- 90.00
The surface of number 1 is a cylindrical surface having a power
only in the auxiliary scanning direction, the surfaces of number 2,
3 and 6 are flat surfaces, the surfaces of numbers 4 and 5 are
toric aspherical surfaces, the surface of number 7 is a cylindrical
surface having a power only in the main scanning direction, the
surface of number 8 is an anamorphic aspherical surface and the
surface of number 9 is a rotationally-symmetrical aspherical
surface.
The toric aspherical surface is defined by the shape in scanning
direction that is represented by the equation (2) and the radius of
curvature in the auxiliary scanning direction rz. The toric
aspherical surface is defined as a locus of the aspherical curve
line defined by the equation (2) when the aspherical curve line
rotates about the axis extending in the main scanning direction
that crosses the optical axis at the point whose distance from the
surface along the optical axis equals to rz.
The various constants and coefficients for defining the toric
aspherical surfaces and the rotationally-symmetrical surface are
shown in TABLE 5. The various constants and coefficients for
defining the anamorphic aspherical surface are shown in TABLE
6.
TABLE-US-00005 TABLE 5 Surface Number .kappa. A.sub.4 A.sub.6
A.sub.8 4 0.00 2.93 .times. 10.sup.-6 2.35 .times. 10.sup.-10 0.00
5 0.00 2.56 .times. 10.sup.-6 3.83 .times. 10.sup.-10 0.00 9 0.00
-3.82 .times. 10.sup.-8 3.35 .times. 10.sup.-12 -3.09 .times.
10.sup.-16
TABLE-US-00006 TABLE 6 .kappa. 0.00 B.sub.1 -1.18 .times.
10.sup.-06 A.sub.4 5.39 .times. 10.sup.-08 B.sub.2 -9.25 .times.
10.sup.-07 A.sub.6 -3.29 .times. 10.sup.-12 B.sub.4 2.30 .times.
10.sup.-11 A.sub.8 6.43 .times. 10.sup.-18 B.sub.6 0.00 A.sub.10
0.00 -- --
FIGS. 10A and 10B are graphs showing the optical performance of the
scanning optical system of the second embodiment; FIG. 10A shows
the linearity error; and FIG. 10B shows the curvature of field.
When the scanning optical systems of the first and second
embodiments are applied to the tandem scanning optical system of
FIG. 4, each of the first and second lenses 51 and 52 is formed as
the complex lens having four lens portions, each of which is
designed according to the data of the embodiments, stacked in the
auxiliary scanning direction, and the third lens 53a designed
according to the data of the embodiments is also employed as the
other third lenses 53b to 53d.
Further, the complex lens is molded by the injection molding of the
resin in the embodiment, while the method of the invention can be
applied to another molding method employing the molding dies, such
as a method to manufacture a glass molding lens or a hybrid lens
having a resin layer on a glass lens.
As described above, since the lens surfaces of the complex lens at
the incident side are formed by the single-piece mirror surface
core and the lens surfaces at the exit side are formed by the other
single-piece mirror surface core, the relative positional error
among the lens surfaces at the incident side and that at the exit
side can be reduced.
Further, when the mirror surface portions have concave sectional
shapes in the auxiliary scanning direction, the boundary portions
can be sharply processed by the cutting tool. Therefore, the mirror
surface portions can be processed without the margins at the
boundary portions, which avoids upsizing of the lens surfaces in
the auxiliary scanning direction more than necessary.
The present disclosure relates to subject matter contained in
Japanese Patent Application No. 2000-358852 filed on Nov. 27, 2000,
which is expressly incorporated herein by reference in its
entirety.
* * * * *